The present invention relates generally to a color plasma display panel (a color PDP) used in a flat panel type television et, a display for displaying information, and the like, and more particularly to a color plasma display panel of a surface discharge type which has a superior white color characteristic and which can display a vivid color image.
A plasma display is a display device which displays an image and so on by exciting fluorescent substance by using ultraviolet rays produced by gas discharge to emit light. The plasma display is expected to be applied to a large picture size television set, an information display, and the like.
Various types of color plasma displays have been developed. As typical types of the color plasma displays, there are a DC pulse memory type display and an AC memory type display. At present, the AC memory type is mainly used industrially because of the lifetime and the luminous efficiency. The AC memory type display is also categorized into an opposed electrode discharge type, a plane discharge type, and the like, depending on the cell structure, the electrode structure and so on. In particular, a reflection type AC surface discharge plasma display is superior in the luminance, easiness of panel fabrication, and the like.
FIGS. 16A through 16C illustrate a panel structure of a typical reflection type AC surface discharge color plasma display. FIG. 16A is an elevational structural view in which a portion of a rear substrate 200 is cut away. FIG. 16B illustrates a structure at a cross section of a front substrate 100. FIG. 16C illustrates a structure at a cross section of the rear substrate 200.
The front substrate 100 which is on the side of a viewer comprises a glass substrate 1 and many band shaped transparent electrodes 3 formed in parallel on the glass substrate 1, in a horizontal direction. On each of the transparent electrodes 3, a bus electrode 4 is formed which bus electrode 4 is a band shaped narrow electrode to lower resistance of the transparent electrode 3. The transparent electrodes 3 are formed of a thin film of ITO (Indium Tin Oxide) or tin oxide. However, the resistance of each transparent electrode 3 should be sufficiently small in order to conduct a discharge current sufficient to emit light in a large size panel, and, therefore, the bus electrode 4 made of metal having good conductivity is attached to each of the transparent electrodes 3 to lower the resistance thereof. The bus electrode 4 is made, for example, of a thick film of silver or a thin film of copper, aluminum, or chromium. On such structure including the transparent electrodes 3 and the bus electrodes 4, a dielectric layer 7 and a protective layer 8 are formed. The dielectric layer 7 is fabricated by applying a low melting point glass paste on the structure including the electrodes 3 and 4, and thereafter baking it at a temperature near 600 degrees Celsius. Thereby, the dielectric layer 7 is formed as a transparent insulating layer having a thickness of approximately 20 through 40 microns. The protective layer 8 is formed by vacuum evaporation and the like, and formed of a thin film of magnesium oxide (MgO) which has a large coefficient of secondary electron emission and has a superior anti-sputtering characteristic.
The rear substrate 200 comprises a glass substrate 2 on which band shaped data electrodes 5 are formed in a vertical direction and, thereafter, a dielectric layer 10 having low melting point glass as the basis is formed thereon. Thereafter, band shaped isolation walls 6 are formed in a vertical direction on the dielectric layer 10. Then, at a bottom portion and side walls of each groove formed by the isolation walls 6, powder type fluorescent substance 9 of red, green and blue colors are sequentially applied, and thereby the rear substrate 200 is completed. The isolation walls 6 secure discharge spaces, and serve to prevent cross talk of discharge and to prevent blotting of emitted light. Approximately, the isolation walls 6 are 30 through 100 microns in width and 80 through 200 microns in height.
The above-mentioned front substrate 100 and the rear substrate 200 are opposed to each other such that the protective layer 8 of the front substrate 100 is opposed to the isolation walls 6 of the rear substrate 200. Both substrates 100 and 200 are then sealed at the periphery thereof by a fritted glass to obtain a panel assembly. The panel assembly is heated and evacuated, and discharge gas having rare gas as the basis thereof is introduced, thereby the plasma display panel is completed.
On the front substrate 100, the transparent electrodes 3 with the bus electrodes 4 are disposed in pairs having a surface discharge gap 11 therebetween. One of the pair of transparent electrodes 3 with bus electrodes 4 is used as a scanning electrode 12, and the other of the pair is used as a retaining or holding electrode 13. Various voltage wave signals are applied to three kinds of electrodes, including the data electrodes 5 mentioned above, in addition to these scanning electrodes 12 and the retaining electrodes 13, thereby the plasma display panel is driven to perform display operation.
FIG. 17 shows an example of waveforms of fundamental drive signals for the AC surface discharge type plasma display panel. Scanning pulses Sc1, Sc2,. . . , ScN are sequentially applied to the scanning electrodes 12-1, 12-2, . . . , 12-N. At the same timing as that of each of the scanning pulses Sc1, Sc2,. . . , ScN, a data pulse Dp is sequentially applied to each of the data electrodes 5 corresponding to a data to be displayed at each display cell. The data pulses have a polarity opposite to that of the scanning pulses. Thereby, a discharge, that is, an opposing electrode discharge, occurs between the scanning electrode 12 and the data electrode 5 opposing to each other. Also, the opposing electrode discharge triggers occurrence of the surface discharge between the retaining electrode 13 and the scanning electrode 12, thereby writing operation is completed. Due to the surface discharge, i.e., a writing discharge, wall charges are produced on the surfaces over the scanning electrode 12 and the retaining electrode 13. In a cell in which wall charges are formed, retaining discharge of the surface discharge, i.e., retaining surface discharge, occurs by retaining pulses Re applied between the retaining electrode 13 and the scanning electrode 12. However, in a cell into which data is not written, retaining discharge does not occur even if the retaining pulses Re are applied, because there is no superimposing effect of electric fields caused by the wall charges. By applying the retaining pulses predetermined times, display of image and so on by light emission is performed.
Also, in order to improve write operation characteristic, a preliminary discharge operation is performed in which a high voltage is applied to all cells before performing write operation, so that any previously stored signals of the cells are erased and discharge is performed forcibly. In FIG. 17, Pd designates a preliminary discharge pulse, and Pe designates preliminary erasure discharge pulse.
As mentioned above, drive operation of a plasma display panel comprises a series of preparing operation, write operation and retained light emission operation. In FIG. 17, a series of such driving operation is shown as an example, in which driving operation of a plasma display panel is separated into a preparing interval in a whole panel, a write interval and a retaining interval. Various driving systems other than the above-mentioned system in which write operation and retain operation are separated can be used, for example, it is possible to use a system in which these operations are mixed. However, when considered in an individual display cell, it is common to these systems that, after preparing operation, write operation is disposed and then retaining operation is disposed.
When tone or gradation of an image and so on is to be displayed in a color plasma display panel, a so-called xe2x80x9csub-field methodxe2x80x9d is used. In the AC type plasma display, it is difficult to modulate luminance of display emission by using voltage control, and, in order to modulate luminance, it is necessary to change number of times of light emission. In the sub-field method, an image of one page is divided into a plurality of pages of binary images and these binary images are continuously displayed in a high speed so that, by using integrating effect of vision, an image having multiple gradation is reproduced.
In a color plasma display panel, ultraviolet rays from xenon atoms or xenon molecules excited by discharge are converted into light of three primary colors by fluorescent substances coated on an inner wall of each cell, thereby color display is realized. Therefore, luminous efficiency and color purity of the fluorescent substances themselves are very important for a plasma display. Ultraviolet rays from xenon mainly include a resonance line of 147 nm or somewhat broad molecular line whose center is 172 nm, and are vacuum ultraviolet rays having very short wavelength when compared with fluorescent lamp which mainly utilizes ultraviolet rays of 254 nm from mercury. Also, it is necessary for the fluorescent substances of color plasma display panel to withstand high temperature during a manufacturing process of the panel, and also the fluorescent substances are directly exposed to plasma. Therefore, usable fluorescent substance is limited at present. As the fluorescent substances 9, (Y, Gd) BO3: Eu and so on is used for emitting red light, Zn2SiO4: Mn and so on is used for green, and BaMgAl10O17: Eu and so on is used for blue, in a practically used panel.
However, the prior art mentioned above has the following disadvantages.
In order to attain good color light emission display, it is important to obtain good white balance characteristic determined by the balance of luminance of respective three primary colors, as well as color purity of each of three primary colors. In a conventional plasma display, color temperature of white color obtained by simultaneously applying retaining pulses to a red cell, a green cell and a blue cell is approximately 6000 degrees Kelvin, and is not so high. Also, with respect to the white balance of this case, white color deviation from the blackbody radiation curve is approximately +0.01 to +0.02 uv, deviating largely toward green color. This is because, luminance of green and luminance of red are relatively high, and luminance of blue is relatively low. In the original NTSC system, color temperature standard of white color is determined to be 6500 degrees Kelvin. However, recently, higher color temperature is preferred to lower color temperature because of vividness of white color, and 9300 degrees Kelvin is used as a reference white color. Also, in a home television, a higher color temperature exceeding 10000 degrees Kelvin is preferred, and such high color temperature has become common in CRT display. In order to realize vividness of display which is comparable to CRT and in order for the color plasma display panel to be widely used, improvement in color temperature of white color and in white color deviation is important and essential.
In a surface discharge type color plasma display in which cells of three primary colors are disposed along surface discharge electrodes as a row electrode, retaining pulses are applied simultaneously to the cells of three colors and it is impossible to apply retaining pulses independently to a cell of each color. Therefore, difference of performance of the fluorescent substance 9 among respective colors directly influences and determines color temperature of white color. Especially, luminous efficiency of the fluorescent substance 9 of blue color is low in comparison with green color and red color, and, therefore, it is impossible to obtain preferred white color having high color temperature. It is important to improve fluorescent material itself, especially to improve luminous efficiency and color purity of the fluorescent substance 9 of blue color. However, improvement in the fluorescent substance is difficult at present, and other measures are considered to obtain preferred white color.
The simplest way is to deliberately lower luminous efficiency of fluorescent substance of green light and/or red light which have relatively high luminance, by controlling thickness of the fluorescent substance or by compounding powder of fluorescent substance. Although this method is easy to implement, ultraviolet rays generated are wasted and therefore luminous efficiency of the plasma display panel is deteriorated.
In another method, color filters are disposed on the display cells of corresponding colors and each color filter is made such that optical density of each color filter is adjusted to obtain proper color balance. Although reflection of external light can be decreased by the effect of the color filters, this method has disadvantages of decreasing luminous efficiency and of increasing manufacturing cost.
In still another method, luminance of each color is adjusted by controlling video signal level of the color. In this case, when white color is displayed, number of light emission, i.e., number of discharges, of the blue cell is made larger than the number of light emission of the green cell and/or the red cell. However, in the color plasma display panel which displays gradation of an image and so on by a digital system of the sub-field method, such method of controlling luminance decreases number of gradations of green color and/or red color whose luminance should be lowered. For example, the number of gradation of blue color is 256 steps, but the number of gradation of green color becomes 200 steps. Especially, since green color contributes relatively large percentage of luminance, if the number of gradations is decreased, disadvantages arise, for example, deterioration of smoothness of image and so on.
It is also possible to change sizes of discharge cells themselves every color so that intensity of light emission of each color is changed accordingly. As shown in FIG. 18, the sizes of discharge cells can be easily changed by changing pitch of the band shaped isolation walls 6. Also, in case of a plasma display panel having rectangular electrode structure, luminance of each color can be controlled by changing pitch of the isolation walls 6, as shown in Japanese patent laid-open publication No. 7-226945. In such example, however, when the plasma display panel is driven to perform display of image and so on, writing characteristics differs every color, and a drive margin to perform good display as a whole panel decreases. Good writing characteristics mean, for example, that data can be written into a cell stably by using a low potential voltage and that, for every color, data can be written into a cell by the same potential voltage.
Considering the problems mentioned above, the present invention has been thought out.
It is an object of the present invention to obviate the disadvantages of a conventional color plasma display panel.
It is an object of the present invention to provide a color plasma display panel in which control of chromaticity of white color can be attained without deteriorating luminous efficiency and drive characteristic.
It is another object of the present invention to provide a color plasma display panel in which display of image and so on at high color temperature can be attained without deteriorating luminous efficiency and drive characteristic.
According to an aspect of the present invention, there is provided a surface discharge type color plasma display panel comprising: a plurality of discharge electrode pairs each of which includes a scanning electrode and a retaining electrode and each of which forms a surface discharge gap between the scanning electrode and the retaining electrode; a plurality of data electrodes disposed perpendicular to the surface discharge gap; and a plurality of display cells each defined at an area including an intersection between the data electrode and the discharge electrode pair. The plurality of display cells are grouped into a plurality of sets of display cells, and each set includes display cells for three primary colors. The discharge electrode pair in each set of display cells has the same shape among the display cells of three primary colors in the proximity of the surface discharge gap, and has different shapes among the display cells of three primary colors at portions remote from the surface discharge gap.
It is preferable that the color plasma display panel further comprises isolation walls which are disposed parallel with the data electrodes and which define discharge spaces of display cells, and that the scanning electrode and the retaining electrode comprise a pair of transparent electrodes.
It is also preferable that an area of the discharge electrode pair in the display cell of blue color is larger than an area of the discharge electrode pair in each of the display cells of other colors.
Further, it is preferable that the scanning electrode and the retaining electrode are a pair of transparent electrodes, and that each of the transparent electrodes has comb like shape in which recessed portions are formed from the surface discharge gap along portions facing isolation walls provided perpendicular to the surface discharge gap.
In this case, end portions of the transparent electrodes on opposite side of the surface discharge gaps may have stepped portions in locations which face portions between the isolation walls, and widths of the transparent electrodes in a direction along the isolation walls may differ every color.
Also, end portions of the transparent electrodes on the side of the retaining electrodes on opposite side of the surface discharge gap may have stepped portions in locations which face portions between the isolation walls, and widths of the transparent electrodes on the side of the retaining electrodes in a direction along the isolation walls may differ every color.
It is preferable that the transparent electrodes have slits which are formed on the portions opposite to the surface discharge gap and at locations facing portions between the isolation walls and whose sizes are changed every color to control color temperature of white color.
It is also preferable that the plasma display panel further comprises bus electrodes which extend parallel to the surface discharge gaps, which are disposed on the outside of the transparent electrodes and on the opposite side of the surface discharge gaps and which are electrically coupled with the transparent electrodes via connecting portions disposed along portions facing the isolation walls, and that there are provided gaps between the transparent electrodes and the bus electrodes, the gaps being provided for changing areas of the discharge electrodes contributing to retaining discharge.
In this case, shapes of the gaps may be changed every color to control areas of said discharge electrodes contributing to retaining discharge.
It is also preferable that the transparent electrodes has recessed portions at location including portions facing the isolation walls which has approximately comb teeth like shape, that tip portions of the transparent electrodes which are not recessed are electrically coupled with the bus electrodes, and that widths, in the direction of the bus electrodes, of the transparent electrodes which are not recessed are different every color.
It is further preferable that the transparent electrodes have transparent electrode portions each of which has approximately rectangular shape, and that lengths of the transparent electrode portions in the direction of the isolation walls differ every color.
The transparent electrodes may have transparent electrode portions each of which has approximately rectangular shape, and each of the transparent electrode portions may have constricted portion on the side of the bus electrode.
Also, the transparent electrodes may have recessed portions on the side of the surface discharge gap and at the location facing the isolation walls, and bus electrodes and the transparent electrodes may be electrically coupled via connecting portions located at portions facing the isolation walls.
In this case, the connecting portions may be formed of a material which is the same as that of the bus electrodes.
Also, the transparent electrodes may have recessed portions on the side of the surface discharge gap and at the location facing the isolation walls, and also may have recessed portions on the side of the bus electrodes toward the surface discharge gap and at the location corresponding to portions between the isolation walls.
It is also preferable that the scanning electrodes and the retaining electrodes are transparent electrodes constituting discharge electrode pairs, that the transparent electrodes have transparent electrode portions which are mutually separated by isolation walls, which have approximately rectangular shape and which have connecting portions having narrow band shape, the transparent electrode portions and bus electrodes are electrically coupled via the connecting portions, and length of the connecting portions differ every color.
It is also preferable that the scanning electrodes and the retaining electrodes are transparent electrodes constituting discharge electrode pairs, that the transparent electrodes have transparent electrode portions which are mutually separated by isolation walls, which have approximately rectangular shape and which have connecting portions for electrically coupling the transparent electrode portions and bus electrodes, and width of the connecting portions differ every color.
It is further preferable that width of each of the data electrodes is wider at portions facing end portions of the scanning electrode on the side of the surface discharge gap than at portions facing other end portions of the scanning electrode on opposite side of the surface discharge gap.
It is also preferable that fluorescent substance of three primary colors are sequentially applied on regions between the isolation walls.